In recent years, for use as a display monitor of a liquid crystal television, a notebook personal computer, a car navigation system, and others, proposed is a liquid crystal display device adopting the VA (Vertical Alignment) mode using a vertically-aligned liquid crystal, for example. In this VA mode, the liquid crystal molecules are each with the negative dielectric anisotropy, that is, the molecules have the properties in which the dielectric constant in the long-axis direction thereof is lower than that in the short-axis direction thereof, thereby realizing the viewing angle wider than that with the TN (Twisted Nematic) mode.
The issue here is that such a liquid crystal display device using the VA-mode liquid crystal causes a problem of varying the luminance between when the display screen is viewed from the front direction and when it is viewed from the diagonal direction. FIG. 14 is a diagram showing the relationship between, in the liquid crystal display device using the VA-mode liquid crystal, the gray-scale (0 to 255 gray-scale levels) of a video signal and the luminance ratio (ratio to the luminance with the 255 gray-scale levels). As indicated by an arrow P101 in the drawing, the luminance characteristics show a large difference (show a variation toward a higher level of luminance) between when the display screen is viewed from the front direction))(Ys(0°)) and when it is viewed from the 45-degree direction (Ys(45°)). Such a phenomenon is referred to as “Shiratchake”, namely, “Wash out”, “Color Shift”, and others, and is regarded as the major drawback of the liquid crystal display device using the VA-mode liquid crystal.
In consideration thereof, as measures to reduce the extent of such a phenomenon of “Wash out”, proposed is the one (multi-pixel structure) with which a unit pixel is divided into a plurality of sub pixels, and the resulting sub pixels are each changed in threshold value (examples include Patent Literatures 1 to 3). The multi-pixel structure described in such Patent Literatures 1 to 3 is called HT (Halftone Gray-scale) technique based on capacity coupling, and any potential difference between two sub pixels is determined by the ratio of capacity.
FIG. 15 is a diagram showing an exemplary relationship between, in the multi-pixel structure, the gray-scale of a video signal and the display state of each of the sub pixels. The drawing shows that, in the process of a change of gray-scale level (an increase of luminance) from 0 (state of black display) to 255 (state of white display), first of all, a part (one sub pixel) of the pixel is increased in luminance, and then the remaining part (the other sub pixel) of the pixel is increased in luminance. With such a multi-pixel structure, as indicated by an arrow P102 in FIG. 14, for example, the extent of the phenomenon of “Wash out” is reduced with the luminance characteristics in the direction of 45° in the multi-pixel structure (Ym(45°)) compared with the luminance characteristics in the direction of 45° in the normal pixel structure (Ys(45°)).
Herein, not only in such a multi-pixel structure but also in the normal pixel structure, the extent of the phenomenon of “Wash out” is known to be reduced with the effects of halftone similarly to the case with the multi-pixel structure by dividing temporally a unit frame of display driving into a plurality of (e.g., two) sub frames, and also by representing any desired level of luminance with a combination of a sub frame(s) of high level of luminance and a sub frame(s) of low level of luminance.